Three dimensional measurement system and pickup apparatus

ABSTRACT

In a three dimensional measurement system, a three dimensional pickup apparatus picks up an object repeatedly to generate image information including a shape of the object, and an information processor receives image frame signals and digital signals from the pickup apparatus to process the image information. Image information is sent as image frame signals through a first output terminal, and digital signals are sent through a second output terminal in correspondence to output of the image information through the first output terminal. In the information processor, an input controller receives the digital signals from the first output terminal and receives the image frame signals suitable for transmission of moving images in correspondence to the received digital signals from the second output terminal. For example, the pickup conditions for a next period are set based on the pickup information obtained in a current period. For example, a distance sensor is provided further to adjust the pickup conditions in various ways in continuous pickup mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and a method for threedimensional measurement wherein a detection light such as a slit lightis cast onto an object to measure a shape of the object.

2. Description of Prior Art

A non-contact typethree dimensional measurement apparatus (threedimensional camera) called as a range finder can measure a shape of amatter at a faster speed than a contact type apparatus. Therefore, it isused as an apparatus for inputting an image for a computer graphic (CD)system or a computer aided design (CAD) system, measurement of amaterial, optical recognition of a robot and the like.

Slit light projection is known as a measurement technique suitable for arange finder, wherein an object is scanned optically and a distanceimage (three dimensional image) is calculated by using the principle oftrigonometry. It is one of active measurement techniques which cast adetection light to pickup an image of an object. A distance image is aset of pixels representing three dimensional positions at a plurality ofpositions on the object. An operation to determine a distance image frompickup information is performed by a range finder itself or by anexternal information processor such as a computer system. In slit lightprojection, a linear slit light is used as the detection light, butother techniques using a spot light, a step light, a density patternlight or the like are also known.

In general, measurement information obtained by a range finder is sentto an on-line information processor or through a storage medium to anoff-line information processor.

Then, it is subjected to predetermined processing such as analysis,edition or storage of the information.

In a prior art range finder, one measurement is performed in response toa command received from the external or to a switch operation by a user.However, if a range finder performs measurements periodically, a rangeof uses of is three dimensional measurement will be expanded. Forexample, it can be used more practically for inspecting a shape of anobject in a production line in a factory, for optical recognition of amoving robot, for a watch system for security guard, or the like. Whendistance images obtained by periodic three dimensional measurements in atime series are compared, a move of an object back and forth or a changein shape can be recognized easily.

However, prior art range finders have problems on repeated pickup. Forexample, in a system where an external information processor gives astart command to a range finder, the external information processor hasto send a start command for each of periodic measurements. Then,communication sequence becomes complicated. Further, in a conventionalthree dimensional measurement system, except in a special system usedonly for displaying a distance image, an information processor performsdata processing such as data analysis and storage. Then, if measurementsare performed periodically, the information processor has to recognizethat the latest measurement information is sent from the range finderand has to store it for data processing.

A prior art portable range finder which can selects a pickup distancehas a sensor for measuring a distance to an object. The measureddistance is used for autofocusing and for setting a range of pickupangle. The distance measurement is performed before optical scanning foreach pickup (or measurement).

In the range finder, active distance measurement can be performedprecisely with use of an optical system for the measurement. Because ithas a scanner, it is easy to expand a viewing angle for distancemeasurement by projecting a light in a plurality of directions. However,if active distance measurement is compared with passive distancemeasurement, a distance range which can be measured is narrower for theactive distance measurement. Then, it is not sure a projection in adirection can catch the object. Then, when the direction of theprojection has to be changed, the measurement time becomes longer.

Because the prior art range finder performs the distance measurement foreach measurement, the measurement time by using the above-mentionedprecise optical measurement is long, especially for the repeatedpickups.

In a prior art range finder, the movement of the lens has to beforbidden during a pickup in order to prevent a change in the pickupconditions. Then, if a distance to an object is changed largely during ameasurement, for example, if the object moves largely during ameasurement, the distance measurement cannot follow the movement of theobject, and a distance measurement controller loses sight of the object.If the object is lost, the measurement conditions such as focusing andlight intensity cannot be set correctly, and the reliability of themeasurement is worsened. Further, if the measurement is performed in adefocused state, the precision of the obtained distance image islowered. Further, if the object is lost, the distance measurement maytake a longer time to catch the object.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a three dimensionalmeasurement system which measures distance images periodically andprocesses data thereof easily and surely.

Another object of the present invention is to provide a threedimensional measurement system which measures distance imagesperiodically and processes data thereof in a shorter time while keepingprecision of the measurement conditions.

A further object of the present invention is to provide a threedimensional measurement system which measures distance imagesperiodically and processes data thereof wherein measurement conditionscan be set appropriately for various uses.

A still further object of the present invention is to provide a threedimensional measurement system which measures distance imagesperiodically and processes data thereof wherein the measurementconditions are set reliably high.

In one aspect of the invention, a three dimensional measurement systemcomprises a three dimensional pickup apparatus which picks up an objectto generate image information including a shape of the object, and aninformation processor which receives image frame signals and digitalsignals from the pickup apparatus to process the image information. Thepickup apparatus comprises an imaging controller for performing pickupoperation repeatedly. It sends image information obtained by the imagingcontroller as image frame signals through a first output terminal, andsends digital signals through a second output terminal in correspondenceto output of the image information through the first output terminal.The information processor comprises an input controller which receivesthe digital signals from the second output terminal and receives theimage frame signals in correspondence to the received digital signalsfrom the second output terminal. When measurement is performedperiodically, because the measured information is image information,image frame signals which have been used for transmission of movingimages are suitable. Such a standard image signal format is advantageousespecially when measurement result (distance image) is displayed with adisplay device in real time for each measurement.

In a second aspect of the invention, a three dimensional pickupapparatus comprises a pick-up device which picks up an object, acondition setter for setting pickup conditions of the pick-up device, animaging controller for performing pickup operation repeatedly in thepickup conditions. The condition setter sets the pickup conditions for anext period based on pickup information obtained in pickup in a currentperiod.

In a third aspect of the invention, a three dimensional pickup apparatuscomprises a distance sensor which measures the distance to the object.That is, distance measurement with the distance sensor is used besidesdistance measurement with light projection using the optical system formeasurement. A pick-up device picks up an object, while a conditionsetter sets pickup conditions of the pick-up device according to adistance to the object. A pickup controller controls the pick-up deviceto pickup the object in the conditions set by the condition setter. Whenthe distance measured by the distance sensor is changed after thecondition setter sets the pickup conditions, the condition setter setspickup conditions again according to the distance measured by thedistance sensor. By using the optical system for measurement, theprecision of the measurement is secured, while by using the distancesensor, continuous measurements are performed. The distance sensor canmeasure the distance in a wider range than the measurement with lightprojection. By selecting a projection direction with reference to themeasured value by the distance sensor, the distance measurement with theoptical system for measurement can be performed efficiently.

In a fourth aspect of the invention, a three dimensional pickupapparatus comprises a pick-up device which picks up an object, acondition setter for setting pickup conditions for setting pickupconditions of the pick-up device, an imaging controller for performingpickup operation repeatedly in correspondence to a start signal. In theperiodic measurement, there are a first case where the measurementconditions have to be kept constant and a second case where measurementconditions have to adjusted for each measurement. The condition settersets the pickup conditions in a first mode before each pickup operationso that each pickup operation is performed in pickup conditions updatedbefore the-pickup operation, while the condition setter sets the pickupconditions in a second mode once so that each pickup operationthereafter is performed in the same pickup conditions. For example, thefirst case includes inspection of a product in a factory, and the secondcase includes optical recognition of a moving robot. If the measurementconditions are fixed, it becomes easy to handle the measurement data intime series, while if the measurement conditions are variable,appropriate measurement data can be obtained irrespective of measurementenvironment. The measurement environment includes a state of a measuredarea including distance to an object, characteristics of the object(reflectivity) and environment light. The measurement conditionsincludes a range of projection angle of detection light, an intensity ofthe detection light and focusing state. Then, it is preferable that auser can select a mode for fixing measurement conditions and a mode forchanging them. On the other hand, if the mode is limited to one of them,the cost can be decreased.

In a fifth aspect of the invention, a three dimensional pickup apparatuscomprises a pick-up device which picks up an object, a condition setterfor setting pickup conditions for the pick-up device, a pickupcontroller for performing pickup operation repeatedly in correspondenceto a start signal. The condition setter sets the pickup conditionsbefore each pickup operation so that each pickup operation is performedin pickup conditions updated before the pickup operation. Pickupinformation obtained in each measurement is used to set measurementconditions for a next measurement. In other words, each measurement isalso used as a preliminary measurement for a next measurement. Then, apreliminary active distance measurement is not needed betweenmeasurements, and the measurement period can be shortened. Because theoptical system for measurement is used for the preliminary measurement,the distance can be measured precisely. Further, because measurementinformation in a number of projection angles is obtained, measurementconditions can be set by using a statistical method or the like.

An advantage of the invention is that a three dimensional measurementsystem can perform periodic measurement without a start command andupdates measurement information surely.

Another advantage of the invention is that the measurement period of athree dimensional measurement system can be shortened in continuousmeasurement mode.

A further advantage of the invention is that the measurement conditionsof a three dimensional measurement system can be set more precisely incontinuous measurement mode.

A different advantage of the invention is that the measurementconditions of a three dimensional measurement system can be set moreprecisely in continuous measurement mode.

A still different advantage of the invention is that the measurementconditions of a three dimensional measurement system can be set moreappropriately according to uses in continuous measurement mode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings, and in which:

FIG. 1 is a diagram of a three dimensional measurement system of theinvention;

FIG. 2A is a perspective view of a three dimensional camera, and

FIG. 2B is a rear view thereof;

FIG. 3 is a block diagram for illustrating functions of the threedimensional camera;

FIG. 4A is a diagram for illustrating a principle of calculation ofthree-dimensional positions in the measurement system, and

FIG. 4B is a graph of the optical intensity plotted against time;

FIG. 5 is a block diagram of an output processor and memories;

FIG. 6 is a diagram for explaining a read range of a sensor;

FIG. 7 is a block diagram of a center-of-gravity operator;

FIG. 8 is a diagram for explaining a relation between an object andpoints in the optical system;

FIG. 9 is a time chart of the three dimensional camera in continuousmode;

FIG. 10 is another time chart of the three dimensional camera incontinuous mode;

FIG. 11 is a time chart of the three dimensional camera in one shotmode;

FIG. 12 is a main flowchart of a system controller of the threedimensional camera;

FIG. 13A is a flowchart of first scan sequence, and

FIG. 13B is a flowchart of second scan sequence;

FIG. 14 is a flowchart of scanning;

FIG. 15 is a flowchart of calculation of projection angle;

FIG. 16 is a flowchart of calculation of slit light intensity;

FIG. 17 is a flowchart of setting; and

FIG. 18 is a flowchart of measurement of a host computer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the views, FIG. 1 showsa diagram of a measurement system 1 according to the inventioncomprising a three dimensional camera (range finder) 2 for performingstereo measurement with slit light projection and a host computer 3 forprocessing data output by the three dimensional camera 2.

The three dimensional camera 2 outputs measurement data (a distanceimage) specifying three dimensional positions of sampling points on anobject 4, a two dimensional image on color information of the object 4and data necessary for calibration. Operation to determine coordinatesof the sampling points by using trigonometry is performed by the hostcomputer 3.

The host computer 3 is a computer system including a central processingunit (CPU) 3a, a display 3b, a keyboard 3c, a mouse 3d, and a memory 3e.The CPU 3a stores a program for processing measurement data. The hostcomputer 3 is online to the three dimensional camera 2 to sent andreceive the data. The memory 3e stores a program for measurement (referto FIG. 18).

FIG. 2A is a perspective view of the three dimensional camera 2. Aprojection window 20a and a light-receiving window 20b are provided at afront of a housing 20. The projection window 20a is located above thelight-receiving window 20b. A slit light U (a laser beam of a linearband of a predetermined width W and a length M1) cast by an internaloptical unit OU (not shown) propagates through the projection window 20ato an object to be measured. Radiation angle φ along the lengthdirection of the slit light U is fixed. A part of the slit light Ureflected by a surface of the object enters through the light-receivingwindow 20b to the optical is unit OU. The optical unit OU has a two-axiscontrol mechanism to adjust relative positions of the projection axisand the light-receiving axis.

At the top of the housing 20 are provided buttons 25a and 25b forzooming, buttons 26a and 26b for manual focusing, and a button 27 forstart/stop. Further as shown in FIG. 2B, at the rear side of the housing20 are provided a liquid crystal display 21, cursor buttons 22, a button23 for selection, a button 24 for canceling, analog output terminals 31and 32 and a digital output terminal 33. A distance image is outputthrough the analog terminal 31 as measurement data, while a twodimensional image DM is output through the other analog terminal 32. Thedigital terminal 33 is for example an RS 232-C terminal and it is usedto output pickup condition data DS. The liquid crystal display 21 isused as a means for displaying images for inputting instructions and asan electronic finder. A user can set a pickup mode by the buttons 22-24at the rear side.

When measurement is performed periodically, because the measurementinformation is image information, image frame signals which have beenused for transmission of moving images are suitable. If a standard imagesignal format such as NTSC format as a representative is adopted, asexplained above, a general circuit for image signal processing can beused and the apparatus can be manufactured at a lower cost. Such astandard image signal format is advantageous especially when measurementresult (distance image) is displayed with a display device in real timefor each measurement.

FIG. 3 illustrates functions of the three dimensional camera 2 whereinsolid lines represent a flow of electric signals and dashed linesrepresent a flow of light. The three dimensional camera 2 has theoptical unit "OU" comprising two optical systems 40 and 50 at theprojection side and at the light-receiving side. In the optical system40 at the projection side, a laser beam of wavelength 670 nm emitted bya laser diode (LD) 41 passes through a projection lens system 42 togenerate the slit light U. The slit light "U" is inclined by agalvano-mirror (scan device) 43. A system controller 61 controls adriver 44 for the laser diode 41, a drive system 42 for the projectionlens system and another drive system 43 for the galvano-mirror.

In the optical system 50 at the light-receiving side, a light collectedby a zoom unit 51 is split by a beam splitter 52. A light in a resonancewavelength band of the laser diode 41 enters to a sensor 53 for distancemeasurement, while a light in a visible light range enters to a monitorcolor sensor 54. The two sensors 53 and 54 are charge coupled device(CCD) area sensors. The zoom unit SO is an internal focus type unit, anda part of the incident light is used for autofocusing (AF) Theautofocusing mechanism is a passive mechanism adopted by single-lensreflex cameras, and it includes an AF sensor 57, a lens controller 58and a focussing drive system 59. A zoom drive system 60 is provided forelectrical zooming. Distance measurement in a passive method by usingthe AF sensor 57 is more advantageous than that in an active method inthat a distance range to be measured is wide and that measurements canbe repeated in a shorter period. However, the precision (resolution) ofthe passive method is not sufficient.

Pickup information obtained with the sensor 53 is transferred to anoutput processor 62 in synchronization with clock signals from thedriver 55. The output processor 62 generates slit data in correspondenceto each pixel in the sensor 53 to be stored in a memory device 63. Acenter-of-gravity operator 64 generates a distance image of highresolution based on the slit data. The distance image is sent through anNTSC conversion circuit 65 as on-line measurement data in a format offrame synchronization image signals. The operator 64 has a control(CTRL) register R1 for storing bit data (GCALC) for control by thesystem controller 61.

On the other hand, pickup information obtained with the color sensor 54is transferred to a color processor 67 in synchronization with clocksignals from the driver 56. The color processor 67 generates pickupinformation (two dimensional image DM) subjected to color processing andsent through an NTSC conversion circuit 70 and the analog terminal 32 asonline data. The two dimensional image DM is a color image having thesame image angle as the distance image obtained with the sensor 53, andit is used by the host computer 3 in the application processing asreference information. The system controller 61 instructs a charactergenerator 71 for displaying characters and signs in correspondence to anoperation state in the liquid crystal display 21.

FIG. 4A illustrates a principle of calculation of a three-dimensionalposition in the measurement system. The slit light U as wide as a fewpixels on a pickup plane S2 on the sensor 53 is cast on the object 4.For example, the width of the slit light U is five pixels. The slitlight U is shifted for each sampling period by one pixel pitch pv fromabove to below on the pickup plane S2, to scan the object. The sensor 53outputs photoelectric conversion information of one field for eachsampling period.

As to a particular pixel g on the pickup plane S2, effectivephotosensitive data are obtained in five samplings among N samplings inthe scan. By performing interpolation on the five photosensitive data, atiming is determined at which the optical axis of the slit light Upasses the surface ag of the object 4 in a range observed by theparticular pixel g. At the timing (or the center-of-gravity of time,N_(peak)), the light intensity detected by the pixel g becomes maximum.In an example shown in FIG. 4B of a graph of the optical intensityplotted against time, the light intensity becomes maximum at a timebetween n-th time and (n-1)-th time before the n-th one. The position(coordinates) of the object 4 is calculated according to a relation ofthe illumination direction of the slit light at the center-of-gravity oftime, N_(peak) to the incident direction of the slit light to theparticular pixel. Thus, measurements can be performed at a higherresolution than that specified by the pixel pitch pv on the pickupplane. The illumination direction of the slit light is determineduniquely by the center-of-gravity of time, N_(peak), if the directionalong which illumination is started and the angle speed of inclinationis known. The incident direction is specified by position relation ofthe sensor 53 to the lens receiving the light.

The light intensity at the particular pixel g depends on thereflectivity of the object 4. However, relative ratios between lightintensities at the five samplings are constant irrespective of theabsolute light intensity. That is, the density of the color of theobject 4 does not affect the measurement precision.

When a distance image is generated from a plurality of pickup images intime series in order to improve resolution of measurement, one image istransmitted for each measurement by transmitting a distance image asmeasurement information, as explained above. Thus, a transmission timeis shortened, and a measurement period can be avoided to become long.Then, measurement can be performed at a high speed and at a highprecision.

In the system 1 of this embodiment, the center-of-gravity of time,N_(peak), is calculated for each pixel g of the sensor 53 by thecenter-of-gravity operator 64 in the three dimensional camera 2, and thecenter-of-gravity of time, N_(peak), of the effective number of pixelsis sent to the host computer 3 in NTSC format. Thus, the amount oftransmitted data becomes smaller by a large extent than a case wherephotosensitive data of five fields are sent to the host computer so thatthe center-of-gravity of time, N_(peak), is calculated by the hostcomputer 3. Thus, a time necessary for serial data transmission ofanalog signals can be shortened. Further, pickup conditions andapparatus conditions necessary to determine coordinates of the objectfrom the center-of-gravity of time, N_(peak), are also transmittedthrough the digital output terminal 33 to the host computer 3 inparallel to the transmission of the distance image.

FIG. 5 is a block diagram of the output processor 62 and memories, andFIG. 6 is a diagram for explaining a read range of the sensor 53. Theoutput processor 62 includes an analog-to-digital (AD) converter 620which converts a photoelectric signal output by the sensor 53 to 8-bitphotosensitive data, four delay memories 621-624 connected in series, acomparator 626, and a generator 627 representing field number (samplingnumber) FN. The memory device 63 includes five memory banks 63A-63E forstoring receive data (slit data) of the effective five fields, a memorybank 63F for storing a field number FN at which the light intensity databecomes maximum, and a memory controller (not shown) for representingaddresses of the memory banks 63A-63F. Each memory bank 63A-63E has acapacity for storing light intensity data of the same number as samplingnumber in a measurement, or the number of effective pixels of the sensor53.

The light intensity data of five fields can be stored in the memorybanks 63A-63E for each pixel g at the same time by delaying data by thefour delay memories 621-624. A read for a field in the sensor 53 isperformed only for an effective light-receiving area (belt-like image)A_(e) in a part of the pickup plane S2. The effective light-receivingarea A_(e) is shifted by one pixel for each field accompanied byinclination of the slit light U. In this embodiment, the number ofpixels is fixed at 32 along shift direction of the effectivelight-receiving area A_(e). A technique to read only a part of an imageon a CCD area sensor is described in Japanese Patent laid openPublication 7-174536/1995.

The AD converter 620 outputs the light intensity data D620 of 32 linesserially in the order of the pixels g. Each delay memory 621-624 is afirst-in first-out (FIFO) memory having a capacity of 31 (=32-1) lines.

The light intensity data D620 of the particular pixel g received fromthe AD converter 620 is delayed by the delays 621 and 622 by two fieldsand is compared by a comparator 626 with a maximum previous data on thepixel g stored in the memory bank 63C. If the delayed data D620 islarger than the maximum previous data, the outputs of the AD converterand the delays 621-624 at the time are stored in memory banks 63E, 63D,63C, 63B and 63A to rewrite the stored contents therein. At the sametime, the field number FN in correspondence to the data D620 stored inthe memory bank 63C is stored in a memory bank 63F.

That is, when the light intensity at the pixel g becomes maximum at then-th field (n<N), the data at the (n-2)-th field is stored in the memorybank 63A, the data at the (n-1)-th field is stored in the memory bank63B, the data at the n-th field is stored in the memory bank 63C; thedata at the (n+1)-th field is stored in the memory bank 63D, the data atthe (n+2)-th field is stored in the memory bank 63E, and the value "n"is stored in the memory bank 63F.

FIG. 7 is a block diagram of the center-of-gravity operator 64 includingfive multipliers 641-645, three adders 646-648, a divider 649 and adelay 640. Weights of -2, -1, 0, 1 and 2 are given to five field numbers(or sampling times) of (n-2), (n-1), n, (n+1) and (n+2) for weightaverage for the light intensity data from the memory banks 63A to 63E.An output of the divider 649, or a weight average, represents a timeshift of n-th sampling time from the center-of-gravity of time, N_(peak)(refer to FIG. 4B). The center-of-gravity of time, N_(peak), is obtainedby adding the time shift to the field number FN from the memory bank63F. The delay 640 is provided to provide the field number FN to theadder 648 at the same time as the time shift, and it delays the fieldnumber FN by a time needed for the weight average.

A distance image DG as measurement information for one processing isgenerated by reading the data for each pixel from the memory banks 63Ato 63E sequentially to send to the center-of-gravity operator 64. Thedistance image DG is output repeatedly for example thirty times persecond.

Next, a basic measurement procedure with use of the three dimensionalcamera 2 is explained. In the three dimensional measurement system 1,the arrangement of the three dimensional camera 2 and an object 4 isvariable. That is, a user can change a pickup distance and an angle foreach pickup application. Therefore, preprocessing (pickup preparation)is performed automatically before measurement in order to set pickupconditions by checking the arrangement with respect to the object 4.

FIG. 8 shows a relation between an object 4 and points in the opticalsystem. When zooming is instructed to the camera 2 by a direct operationby a user or with a remote operation by the host computer 3, a variatorof the zoom unit 51 is moved, and a focusing section thereof moves thelens for focusing. During the focusing, a rough estimate of the distanced_(o) to the object 4 is obtained. In correspondence to the lens driveof the light-receiving system, a move distance of the variator lens atthe projection side is calculated, and the lens movement is controlledaccording to the result of the calculation. However, zooming andautofocusing are forbidden during a pickup in order to prevent thatpickup conditions are changed by the movement of the lens.

The system controller 61 reads an output (moving value Ed) of an encoderin the autofocusing drive system 59 an output (zoom setting value fp) ofan encoder in the zooming drive system 60. Inside the system controller61, distortion aberration table, main point position table and imagedistance table are referred, and pickup condition data in correspondenceto the moving value Ed and the zoom setting value fp are sent to thehost computer 2. The pickup condition data includes a main pointposition at the front side, and a distance of the image. Further, thesystem controller 61 calculates an output (laser intensity) of the laserdiode 41 and inclination conditions of the slit light U (projectionstart angle, projection stop angle and inclination angle speed).

In the preprocessing, first, the projection angle is set so as toreceive the reflected light at the center of the sensor 53 by assumingthat a plane object exists at the estimated distance do to the object 4.

Next, laser intensity is calculated. By taking safety for human bodyinto account, the laser diode 41 emits a pulse beam at the minimumintensity and an output of the sensor 53 is received. The projectionangle has been set based on the distance d_(o) to the object 4. A ratioof the received output signal to an appropriate level is calculated, anda temporary laser intensity is set. Then, the laser diode 41 emits apulse beam again at the temporary intensity, and an output of the sensor53 is received. The temporary setting of the laser intensity and theconfirmation that the laser intensity is allowable are repeated untilthe output of the sensor 53 becomes within an allowable range. If theoutput of the sensor 53 is not sufficient even if the laser diode 41emits a beam at the maximum intensity, exposure is controlled tolengthen the charge storage time of the sensor 53.

Next, the distance d to the object 4 is determined with trigonometrybased on the projection angle of the slit light U and the position toreceive the reflected light. The calculation of the inclinationconditions takes into account the offset d_(off) of the main point H' atthe rear side of the light receiving system as a reference point formeasurement the distance d relative to the start point A of projection.In order to secure the same allowable range of distance measurement atthe end in the scan direction as at the center, over-scanning isperformed by a predetermined quantity such as eight pixels. Theprojection start angle th₁, the projection stop angle th₂, andinclination angle speed ω are obtained with the following equations:##EQU1## wherein β denotes pickup magnification power (=d/f_(real)),f_(real) denotes effective focal distance, pv denotes pixel pitch, npdenotes effective pixel number in the horizontal direction in the pickupplane S2 and L denotes length of base line.

    ω=(th.sub.1 -th.sub.2)/np                            (3)

An actual measurement is performed in the conditions calculated above,and apparatus information and pickup conditions including thespecifications of the sensor 53 are sent to the host computer 3 besidesthe distance image DG. However, in the continuous mode explained later,the apparatus information is sent only at the first time of themeasurement. Table 1 compiles main data sent by the three dimensionalcamera 2 to the host computer 3.

                  TABLE 1                                                         ______________________________________                                        Data sent to the host                                                         Contents of data         Data range                                           ______________________________________                                        Measurement data                                                                          Distance image                                                                (Analog video signal)                                             Pickup conditions                                                                         Image distance b  0.00-300.00                                                 Main point FH at the front                                                    side                                                                          Projection start angle th.sub.1                                               Inclination angle speed ω                                   Apparatus information                                                                     Numbers of pixels                                                                                  1-0.00516                                                (Sampling numbers,                                                            X and Y directions)                                                           Pixel pitches pu, pv                                                          Attitude of projection system                                                                     0.00-±90.00                                            (around X, Y and Z axes)                                                      Attitude of projection system                                                                     0.00-±300.00                                           (in X, Y and Z axes)                                                          Lens distortion correction                                                                      0.00-256.00                                                 factors d1 and d2                                                             Sensor center pixel u0 and v0                                     2-dimensional image                                                                       Analog video signals (Color)                                      ______________________________________                                    

Next, the operation of the measurement system 1 is explained further indetail.

The three dimensional camera 2 has one shot mode where measurement isperformed only once in response to the start command and continuous mode(continuous pickup mode) where measurements are repeated after a startcommand until a stop command is issued.

The continuous mode has variable mode and fixed mode as autofocusingmodes. In the variable mode, autofocusing is performed in correspondenceto an output of the AF sensor 57 except measurement periods. In thefixed mode, autofocusing is performed only at the first measurement. Themeasurement of the distance to the object is performed constantly by theAF sensor 57 in each of the modes. When the magnification power of thepickup is large, defocusing is liable to occur. Then, the variable modeis appropriate to get a clear distant image. Further, in the variablemode, the position of the object can be detected when it moves largely.On the other hand, driving control for the lens can be omitted in thefixed mode.

As explained above, distance measurement with a distance sensor is usedbesides distance measurement with light projection using an opticalsystem for measurement. By using the optical system for measurement, theprecision of the measurement is secured, while by using the distancesensor, continuous measurements are performed. The distance sensor canmeasure the distance in a wider range than the measurement with lightprojection. By selecting a projection direction with reference to themeasured value by the distance sensor, the distance measurement with theoptical system for measurement can be performed efficiently.

                  TABLE 2                                                         ______________________________________                                        Contents of control signals                                                   Items       Contents                                                          ______________________________________                                        RUN         Completion of pickup preparation                                  SStart      Command for execution of measurement                              GCALC       Center of gravity operation                                       NextI       Start of output of latest image                                   VSync       Frame synchronization signal of image output                      Frame counter                                                                             Counter of VSync signals                                          OPR         Output period of distance image                                               (Frame number)                                                    ______________________________________                                    

FIGS. 9 and 10 are time charts of the three dimensional camera 2 in acontinuous mode. Table 2 shows the contents of control signals. In Table2, RUN, SStart, GCALC and NextI represent bits in the control registerR1, and OPI is shown as "i" in FIGS. 9 and 10.

The operation of the system controller 61 is explained here. At point[1], pickup preparation (preprocessing) is started, in correspondence topressing the start/stop button 27 or an input of start command by thehost computer 3. In the preparation, the distance d to the object 4 isdetermined with the above-mentioned light projection, and varioussettings such as active autofocusing (A-AF), projection angle and laserintensity are performed.

At point [2], or when the pickup preparation is completed, RUN bit inthe control register R1 is set at 1. Then, it is waited that SStart bitbecomes 1.

At point [3] or at the first VSync signal after the RUN bit becomes 1,SStart bit is set at 1, and the frame counter is reset. The SStart bitis reset at 0 at the next VSync signal.

At points [4] and [5], or when SStart bit becomes 1, the movement of thelens is inhibited to keep pickup conditions fixed, and the scanning(pickup) of the object is started with the slit light "U". In a periodof about 0.8 second thereafter, the system controller 61 only controlsthe scanning, and the lens controller 68 measures the distance with theAF sensor 57. In the measurement, the distance to the object at thestart of the next scanning can be predicted according to the change inthe distance to the object.

At points [6] and [7], or when the scanning is completed, GCALC bit inthe control register R1 is set at 1. Then, the center-of-gravityoperator 64 starts to calculate the center-of-gravity of time N_(peak).The GCALC bit is reset at 0 when the distance image DG is generatedcompletely.

The movement of the lens is allowed for the lens controller 58. Then,the lens controller 58 starts passive autofocusing (P-AF) to measure thedistance to the object with the AF sensor 57.

At points [8] and [9], or at the first VSync signal after the GCALC bitreset at 0, NextI bit is set at 1, and the frame memory is changed tostart the output of the latest distance image. Then, the distance imageDG of the same content is output repeatedly until a new distance imageis generated. The NextI bit is reset at 0 at the first VSync signalafter NextI bit is set at 1.

Then, at point [10], pickup conditions and apparatus information aresent from a port (the digital output terminal 33) different from theport for the distance image DG to the host computer 3. Thus, the hostcomputer 3 recognizes that the latest distance image DG is output. Afterthe data output is completed, distance conditions and exposureconditions are calculated for a next pickup based on the present pickup,and it is waited that SStart bit becomes 1. At this stage, if thevariable mode is set, a change in the distance to the object is detectedaccording to the output of the passive autofocusing. If the changeexceeds a threshold, the distance is measured precisely with lightprojection, and focusing and pickup conditions are calculated.

At point [11], or when the count of the frame counter becomes a valuesmaller by one than the predetermined value (OPR), the count is reset atthe next VSync signal, and the SStart bit is set at 1. Then, the SStartbit is reset at 0 at the next VSync signal. The value OPR is setmanually with the host computer 3. That is, a user can set a desiredmeasurement period.

At points [12] and [13], or when the SStart bit becomes 1, the movementof the lens is inhibited to keep pickup conditions fixed, as at points[4] and [5], to start scanning (pickup). Thereafter, operations between[6]-[11] are performed, and measurement between points [3]-[11] arerepeated each time the SStart bit becomes 1. However, the output of theapparatus information is omitted at the second measurement after thestart instruction and thereafter.

As shown in FIG. 10, at points [14] and [15], or when the start/stopbutton 27 is pressed again or a stop command is received from the hostcomputer 3, the RUN bit is reset at 0. If the stop command is receivedduring the center-of-gravity operation, the GCALC bit is reset at 0 atthe time. The output of the latest distance image is repeated when thestop command is issued at any time.

FIG. 11 is a time chart of the three dimensional camera 2 in the oneshot mode. At points [21]-[29], similar operation to the points [1]-[9]in the above-mentioned continuous mode is performed.

At point [30], the RUN bit is reset at 0 when the NextI bit becomes 1.

At point [31], pickup conditions and apparatus information are outputthrough the digital output terminal 33 to the host computer 3.Thereafter, a start command is set, and the output of the latestdistance image is repeated until a new distance image is generated.

FIG. 12 is a main flowchart of the system controller 61 of the threedimensional camera 2. When the power supply is turned on, controlparameters including bits in the control register R1 are set forinitialization (step #1). Then, the mode is set according to the buttonoperation or a command from the host computer 3 (step #2). Thus, a usercan set the measurement period in the continuous more in the unit offrame.

When a start command is received, measurement is started (step #3). Ifthe mode is variable mode, the first scan sequence is performed (steps#4 and #5), while if it is fixed mode, the second scan sequence isperformed (step #6). FIG. 13A is a flowchart of the first scan sequence(FIG. 12, step #5), and FIG. 13B is a flowchart of the second scansequence.

In the first scan sequence, shown in FIG. 13A, passive autofocusing isstarted first, and the position of the focusing lens is controlledaccording to the relative movement of the object to the threedimensional camera 2 (step #51). When a start command is received,passive autofocusing is stopped to prevent movement of the lens duringscanning (step #52), and zooming is inhibited (step #53).

Then, scanning for obtaining a distance image DG is performed (step#54). After the scanning is completed, passive autofocusing is startedagain (step #55), and inhibition of zooming is canceled (step #56).Commands and operations are accepted (step #57), and it is waited thatthe count of frame synchronization signals VSync attains a predeterminedvalue (step #58). Then, it is decided if the measurement is completed ornot (step #59). In the one shot mode, or when a stop command is receivedin the continuous mode, the flow returns to the main routine. If a stopcommand is not received in the continuous mode, the flow returns to step#52 to repeat measurement.

In the second scan sequence (FIG. 12, step #6), shown in FIG. 13B,passive autofocusing is started first (step #61). When a start commandis received, passive autofocusing is stopped to prevent movement of thelens during scanning (step #62), and zooming is inhibited (step #63).Then, scanning for obtaining a distance image DG is performed (step#64). After the scanning is completed, inhibition of zooming is canceled(step #65), but passive autofocusing is not started again. Commands andoperations are accepted (step #66), and it is waited that the count offrame synchronization signals VSync attains a predetermined value (step#67). Then, it is decided if the measurement is completed or not (step#68). In the one shot mode, or when a stop command is received in thecontinuous mode, the flow returns to the main routine. If a stop commandis not received in the continuous mode, the flow returns to step #63 torepeat measurement.

FIG. 14 is a flowchart of scanning (FIG. 13A, step #54 and FIG. 13B,step #64). As explained above, the distance to an object 4 to bemeasured is measured always with the sensor 57. A change in the distanceis checked, and if the change exceeds a threshold (YES at step #100),setting is performed to determine pickup conditions by determining thedistance to the object with slit light projection (step #101). Even ifthe change does not exceed a threshold (NO at step #100), if themeasurement is the first measurement performed after a start command(YES at step #102), the scanning is performed. In other words, in themeasurements after the first measurement, the setting is omitted if thechange in distance is not large. Thus, the precision of the threedimensional measurement is assured, and the load of the measurementcontrol is decreased.

If distance calculation mode is set as a setting mode for pickupconditions in the continuous mode (YES at step #103), scanning controlis performed to obtain a distance image in the pickup conditions set atthe time (sep #104), and projection angle and slit light intensity arecalculated based on the pickup information to be provided forcalculating pickup conditions in the next measurement (steps #105 and106).

If brightness calculation mode is set as a setting mode for pickupconditions in the continuous mode (YES at step #107), scanning controlis performed to obtain a distance image in the pickup conditions set atthe time (sep #108), and slit light intensity is calculated based on thepickup information to be provided for calculating pickup conditions inthe next measurement (steps #109).

If neither of distance calculation mode or brightness calculation modeis set as a setting mode for pickup conditions in the continuous mode(No at step #107), only the scanning control is performed (step #110).

In this embodiment, the pickup information obtained in each measurementis used for setting light-receiving conditions for a next measurement.In other words, each measurement is also used as a preliminarymeasurement for a next measurement. Then, a preliminary active distancemeasurement is not needed between measurements. If this scanning iscompared with a prior art where pickup conditions are measured for eachmeasurement by using preliminary measurement, the measurement period canbe decreased by a time needed for the preliminary measurement becausepickup conditions in the next measurement are calculated based on thepickup information just before the measurement. Because the opticalsystem for measurement is used as the preliminary measurement, thedistance can be measured precisely. Further, because measurementinformation in a number of projection angles is obtained, detailedinformation can be obtained on the space to be scanned in themeasurement, and pickup conditions can be calculated more precisely byusing the measurement information in each time as preliminarymeasurement information for the next information than the preliminarymeasurement which uses projection of the slit light in one direction.

FIG. 15 is a flowchart of calculation of projection angle (FIG. 14, step#105). First, the distance image is analyzed, and a representative valueof the distance to the object is determined (step #1051). Therepresentative value can be determined in various ways including threemethods explained below. In the first method, pixels are sampleduniformly in the entire image, and the shortest distance is selected asthe representative value. This can avoid an error that a distance to thebackground in the image is selected as the representative value. In thesecond method, a plurality of pixels aligned vertically and horizontallyaround the center of the image are sampled, and an average of anintermediate value of the distances is determined as the representativevalue. This is advantageous that the effect of noises is small. In thethird method, the first and second methods are combined so as to samplea plurality of pixels aligned vertically and horizontally in each areaobtained by dividing the image uniformly.

Next, an actual distance is calculated based on the apparatus conditionssuch as the representative value and the pixel pitch and the pickupconditions such as focal distance by applying trigonometry (step #1052).Then, start angle and stop angle of the projection in the scanning areset so that a predetermined area before and behind the position of theobtained distance is measured.

FIG. 16 is a flowchart of calculation of the slit light intensity (FIG.14, steps #106 and #109). The light intensity (quantity of reflectedlight) data of the n-th field stored in the memory bank 63C in thememory 63 is sampled uniformly, and the largest value is set as arepresentative value (step #1061). If the largest sampled value is theupper limit value, or if the light intensity measured by the sensor 53is saturated, the largest light intensity is measured by interpolationwith light intensity data of the pixels under interest at the (n±1)-thfields, and the result is set as the representative value.

Next, the slit light intensity is adjusted according to therepresentative value so that the light intensity detected by the sensor53 is most appropriate (step #1062). If necessary, the exposure time ofthe sensor is also adjusted to make the light intensity detected by thesensor 53 most appropriate. As explained above, the light-receivingconditions are adjusted according to the pickup information obtained ina previous measurement. Thus, each measurement is also used as apreliminary measurement for the next measurement.

FIG. 17 is a flowchart of the setting (FIG. 14, step #101). If a pickupdistance is not specified with manual operation or by a command (NO atstep #1011), the slit light "U" is emitted (step #1012), and thepickuped image is read (step #1013), and the distance to the object isdetermined at IS based on the pickup information, and the start angleand stop angle of the projection in the scanning are set so that a,predetermined area before and behind the position of the obtaineddistance is measured (step #1014). If the light intensity is notspecified (NO at step #1015), the flow proceeds to step #1019.

If the pickup distance is specified but the light intensity is notspecified (NO at step #1016), the slit light "U" is emitted (step#1017), and the pickup image is read (step #1018). Then, the intensityof the slight light "U" is adjusted according to the obtained pickupinformation so that the light intensity detected by the sensor 53becomes most appropriate (step #1019).

FIG. 18 is a flowchart of measurement performed by the host computer 3.First, a start command is sent to the three dimensional camera 2 (step#31), and pickup condition data DS is waited to be sent (step #32). Thedistance image DG is get as measurement information for a measurement incorrespondence to the input of the pickup condition data DS (step #33).Then, the information processing is performed on the distance image(step #34). The information processing includes coordinate calculationbased on the distance image DG and the pickup conditions and write ofthe distance image DG to a recording medium. The latest distance imageDG is get repeatedly in correspondence to the input of the pickupconditions data DS until predetermined stop conditions (time and anumber) are satisfied (step #35).

When the predetermined stop conditions are satisfied, a stop command issent to the three dimensional camera 2 (step #36), and the measurementis completed. A user may monitor the measurement situation by displayingthe distance image on the display 3b of the host computer 3. It is alsopossible to display two-dimensional pickup image beside the distanceimage DG.

In the above-mentioned embodiment, the pickup condition data DS are usedas a control signal for getting the distance image DG. If themeasurement period does not agree with the frame period of the imagesignal format, it is necessary to send a signal for receivingmeasurement information besides the frame synchronization signals.Because digital signals on measurement conditions or the pickupcondition data DS are used as the signal, it is not necessary forproviding a special signal for getting the distance image. A user canchange the measurement period in the continuous mode in the unit offrame.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

What is claimed is:
 1. A three dimensional pickup apparatus which picksup an object to generate image information including a shape of theobject, said apparatus comprising:a pick-up device which picks up anobject; a condition setter for setting pickup conditions of the pick-updevice; an imaging controller for performing pickup operation repeatedlyin correspondence to a start signal; wherein said condition setter setsthe pickup conditions in a first mode before each pidkup operation sothat each pickup operation is performed in pickup conditions updatedbefore the pickup operation and said condition setter sets the pickupconditions in a second mode once so that each pickup operation isperformed in the same pickup conditions.
 2. The three dimensional pickupapparatus according to claim 1, wherein said condition setter sets thepickup conditions according to a position of the object relative to saidthree dimensional pickup apparatus.
 3. The three dimensional pickupapparatus according to claim 2, wherein said pick-up device comprises aprojection unit which projects a slit light to an object while changinga projection angle of the slit light and a light-receiving unit whichreceives a light reflected by the object, and said condition setter setsan intensity of the projection light as one of the pickup conditions. 4.The three dimensional pickup apparatus according to claim 1, whereinsaid pick-up device comprises a projection unit which projects a slitlight to an object while changing a projection angle of the slit lightand a light-receiving unit which receives a light reflected by theobject, and said condition setter sets a range of the projection angleof said projection unit as one of the pickup conditions.
 5. A threedimensional pickup apparatus which picks up an object to generate imageinformation including a shape of the object, said apparatus comprising:apick-up device which picks up an object; a condition setter for settingpickup conditions of the pick-up device; and a pickup controller forperforming pickup operation repeatedly in correspondence to a startsignal; wherein said condition setter sets the pickup conditions beforeeach pickup operation so that each pickup operation is performed inpickup conditions updated before the pickup operation.
 6. The threedimensional pickup apparatus according to claim 5, wherein saidcondition setter sets the pickup conditions according to a position ofthe object relative to said three dimensional pickup apparatus.
 7. Thethree dimensional pickup apparatus according to claim 5, wherein saidpick-up device comprises a projection unit which projects a slit lightto the object while changing a projection angle of the slit light and alight-receiving unit which receives a light reflected by the object, andsaid condition setter sets a range of the projection angle of saidprojection unit as one of the pickup conditions.
 8. The threedimensional pickup apparatus according to claim 5, wherein said pick-updevice comprises a projection unit which projects a slit light to theobject while changing a projection angle of the slit light and alight-receiving unit which receives a light reflected by the object, andsaid condition setter sets an intensity of the projection light as oneof the pickup conditions.
 9. A three dimensional pickup apparatus whichpicks up an object to generate image information including a shape ofthe object, said apparatus comprising:a pick-up device which picks up anobject; a condition setter for setting pickup conditions of the pick-updevice; an imaging controller for performing pickup operation repeatedlyin correspondence to a start signal; wherein said condition setter setsthe pickup conditions once so that each pickup operation is performed inthe same pickup conditions thereafter.
 10. The three dimensional pickupapparatus according to claim 9, wherein said condition setter sets thepickup conditions according to a position of the object relative to saidthree dimensional pickup apparatus.
 11. The three dimensional pickupapparatus according to claim 9, wherein said pick-up device comprises aprojection unit which projects a slit light to an object while changinga projection angle of the slit light and a light-receiving unit whichreceives a light reflected by the object, and said condition setter setsa range of the projection angle of said projection unit as one of thepickup conditions.
 12. The three dimensional pickup apparatus accordingto claim 9, wherein said pick-up device comprises a projection unitwhich projects a slit light to an object while changing a projectionangle of the slit light and a light-receiving unit which receives alight reflected by the object, and said condition setter sets anintensity of the projection light as one of the pickup conditions.